Thin dielectric films are utilized in a wide variety of device applications, ranging from protective layers in semiconductor circuits, computer read-write heads, magnetic media, and displays, to components in optical waveguides, mirrors, filters and switches. What is common about all these applications is that these dielectric layers must be as free from defects as possible so that they provide a high level of insulation between current-carrying conductors sandwiched around them.
For many applications fairly thick (several microns) dielectric films are required, so it is desirable to have a production-worthy deposition scheme that will be capable of producing high quality dielectric films at high rates. Traditionally, RF diode or RF magnetron sputtering from insulating targets is used for dielectric coating. However, the deposition rates afforded by such techniques is extremely low, and it can take several hours to deposit even a relatively thin film. Another disadvantage of RF sputtering is that the process is very hot, and can damage fragile substrates.
DC reactive magnetron sputtering from metallic targets is an excellent way of boosting dielectric deposition rates. Advantages of this technique over RF include 1) 5–10 times higher rates, 2) cooler processes, 3) less flaking from metallic targets, leading to lower defect densities on the substrate, provided arcing is well-suppressed, and 4) simpler and less expensive power supplies. The main disadvantage is that, for a magnetron cathode which has a limited area of erosion, DC reactive sputtering leads to dielectric layer buildup on areas of the target that are not eroded. This in turn leads to arcing, particles and defect formation in the deposited films. An advanced arc-suppression scheme, such as that utilized in Advanced Energy's Pinnacle Plus switching power supply, needs to be used for DC reactive deposition of dielectric films from conventional cathodes. However, such power supplies approach the expense and complexity of a RF scheme.
It is, therefore, critically important in DC reactive deposition of dielectric films to have a cathode that provides full-face erosion of the target surface. A moving magnetron cathode is one of the best ways of achieving such full-face erosion. An example of such a cathode that has been successfully utilized for arc-free DC reactive deposition of dielectric films is S. Hurwitt's U.S. Pat. No. 5,130,005, which describes a rotating magnetron scheme for a circular cathode. However, this cathode cannot be utilized in a scanning, in-line batch tool. Another moving magnetron patent has been issued to McKelvey in U.S. Pat. No. 4,422,916, which describes a rotating cylindrical magnetron. The disadvantage of this type of cathode is that it is very difficult to fabricate cylindrical targets from brittle materials. A rectangular planar magnetron with a moveable magnet assembly is known from U.S. Pat. No. 4,444,643, in which the magnetic assembly is translated laterally and parallel to the major axis of the target. DE-A-27 07 144 proposes a magnet assembly which is swept over a rectangular target along a linear path. U.S. Pat. No. 4,714,536 proposes that the magnet assembly is moved with a non-repetitive small epicycloidal motion distributed over the area of the target. U.S. Pat. No. 5,188,717 explains that even erosion of the target can be obtained when the dwell time of the magnetic flux remains equal over each unit area of the target and proposes a specific shape to the magnet assembly. U.S. Pat. No. 5,382,344 describes a magnet assembly which produces electron paths in a plurality of racetracks which are moved linearly and perpendicularly to the longest axis of the target with an oscillatory motion. EP-A-416 241 describes a magnet array which may be moved in an oscillating motion limited by the cathode tray, the motion being produced by a pin on a rotating cam, the pin being journalled in the base of the rotating cam. U.S. Pat. No. 5,328,585 describes a linear planar-magnetron cathode with a reciprocating magnet array, where the reciprocating motion can be simultaneously lateral and longitudinal with respect to the cathode. U.S. Pat. No. 5,833,815 proposes reciprocating motions parallel to the substrate moving direction and at an angle thereto. U.S. Pat. No. 5,417,833 discusses previous attempts to achieve full target erosion, and combines a rotating permanent magnet array with an stationary electromagnet. This scheme is extremely complex and difficult to apply to a wide range of applications. U.S. Pat. No. 6,494,999 describes a magnetron cathode assembly that can be scanned over the target assembly, independent of vacuum or vacuum components. The target assembly includes heating/cooling passages and a heat exchanger/pressure relieving plate. The patent describes much more about the integral cooling and pressure relief mechanism than the actual magnet design and performance of the cathode. U.S. Pat. No. 6,416,639 reviews most of the aforementioned patents and describes a technique for combining a moving magnet array with fixed ferromagnetic pole pieces to smooth out the erosion profile.
The object of the present invention is to provide a simple, practical and effective means of achieving near-complete target erosion over a rectangular cathode in an in-line batch sputtering system. This means should be applicable to a wide range of target materials and processes. In particular, DC reactive sputtering of dielectrics should be easily effected without recourse to expensive and complex arc-suppression circuitry. Target utilization should be over 70%, thus providing a cost-effective solution for the use of precious metal and other expensive targets.